The categorical imperative is strictly weaker: It's possible to use the veil of ignorance to argue against positions
nobody is insisting must be made universal.
For example, "In this house, you always clean up": The categorical imperative only works to argue against this if you try to find a way to apply it to every household; the veil of ignorance works simply by forcing the members of the household to be ignorant about who 'you' refers to.
